Safety control switch



July 6, 1954 K. E. SPIRES, JR

SAFETY CONTROL SWi'TCH Filed Dec. 6, 1952 Patented July 6, 1954 UNITED STATES OFFICE 9 Claims. (Cl. 200113) This invention relates to a safety control switch for breaking the circuit to an electrically operated device in response to overload current demands of the device, such as a safety control switch for an electric motor.

An object of the invention is to provide a safety control switch having a thermally responsive mechanism responsive to current flow to an electrically operated device for opening an electric circuit to the device quickly in response to high overload conditions or current surge to the device and to open a circuit to the electrically operated device in a delayed manner in the event of a lesser prolonged overload current flow to the electrically Fig. 2 is a cross sectional view of a portion of the mechanism of Fig. 1, illustrating a normal position of the thermally responsive mechanism;

Fig. 3 is a cross sectional view similar to Fig. 2, but illustrating the positions of the primary and secondary bimetal members on a quick release of the control switch;

Fig. 4 is a cross sectional view similar to Figs. 2 and 3 but illustrating the positions of the primary and secondary bimetal members upon effective modification of the position of the primary member by the secondary member;

5 is a cross sectional view similar to Figs. 2, 3 and 4, but illustrating the released position of operated device, the safety control switch thus t e primary and secondary bimetal members having one quick acting release feature and eiiected from the modified position of the memanother slow acting release feature which are 'ccl'sas l us ated in ig. effective dependent upon the type of current load Fig. 6 is a cross sectional View of a modified carried by t electrically operated device construction of the safety control switch.

th object, of the invention is to provide When providing for breaking of an electric a safety control switch for breaking an electric circuit the electrically operated device, such as circuit to an electrically operated device such as electric motors, because of overloaded conditions an electric motor, wherein there is provided a on the electrically operated device, there are two first thermally responsive bimetal member that independent conditions that must be considered is responsive to current flow to the electrically and taken care of. operated device for quickly releasing the safety For example, there is one overload condition control switch to break circuit to the electrically for an electric motor that results in a surge of operated device on a sudden surge of current to electric current to the electric motor, such as a the device, and which is provided with a second walled condition, or under extremely heavy overthermally responsive bimetal member th t is load. In this situation it is essential that the thermally responsive from the first bimetal memelectric current be disconnected from the electric her to cause modification of the eiifect of the motor quickly to eliminate damage to the motor. first bimetal member to delay release of the There is also a second type of overload condisafety control switch as a result of prolonged tion caused in an electric motor, such as when overload to the electrically operated device resultthe motor is operated under a medium overload ing in a slow temperature increase of the primary condition, causing a current fiow less than the bimetal member. high current surge required for quick release of Another object of the invention is to provide the safety control switch to break control to the a safety control switch responsive to current flow electric motor. This medium overload condition to an electrically operated device wherein a priwill result in a gradual temperature increase of mary bimetal member is modified in its effective the motor and the electric circuit must be broken action by a secondary bimetal member in a manto the electric motor within a reasonable time or her to increase the trip time of the primary damage will result to the motor. bimetal member upon ellective actuation of the However, if a safety control switch or thermal secondary bimetal member in response to temoverload control, is initially set up for giving a perature increase of the secondary bimetal memquick response to a high current surge, the effecberfromthe primary bimetal member. tive temperature increase of the bimetal mem- Further objects and advantages of the present her that actuates the device would result in the invention will be apparent from the following same kind of response in the event of a medium description, reference being made to the accomcurrent overload, the initial deflection of the panying drawings wherein a preferred embodibimetal member depending entirely up l the ment of the present invention is clearly shown. temperature increase, which for sudden current In the drawings: surges is maintained at a relatively low volume. Fig. 1 is a cross sectional view of a safety con- However, an electric motor can p ate sat strol switch incorporating the feature of this factorily under a medium overload condition for invention;

a relatively prolonged period of time, but if continued indefinitely, will result in damage to the motor. Thus, it is essential that the thermal overload control also be responsive to a gradual temperature increase of the motor resulting from a medium overload operating condition, but the response of the thermal overload control in breaking circuit to the electric motor should be over a much longer period of time and be ineffective until the motor has reached a dangerous opera-ting temperature.

In this event, therefore, the safety control switch, or thermal overload control, is provided with one bimetal member that normally responds quickly to a high current surge to cause release of the overload mechanism and a second bimetal member is responsive to the temperature of the first bimetal member to cause a modified setting of the first bimetal member resulting in a delayed action of the first or primary member until the temperature rise resulting from the continued flow of overload current is sufiicient to deflect the primary member for release of the thermal overload mechanism.

One form of the mechanism as illustrated in the drawings consists of a housing ll] constructed of insulating material and having a hollow interior H. Contacts [2 and [3 are provided in series circuit with an electric motor l4, the contacts having a bridging element l5 for completing circuit through the electric motor in a manner hereinafter described.

The bridging member is carried on an operating rod l6 journaled in walls II and is of the housing [0. The operating member carries a spring 19 that engages the bridging member 15 to push th same against the contacts l2 and 13 when the mechanism is in the position illustrated in Fig. 1. The operating member I6 is engaged by an actuating device 20, the operating member I6 extending through an opening in the actuating device 20 and having knife edges 2! and 21a that form a pivot connection between the operating member 16 and the actuating device 20.

The actuating device 26 is pivotally mounted on a pivot pin 22 secured to the wall 23 of the housing ID. A coil spring 24 has one end thereof engaging a stationary pin 25 and the other end thereof engaging the actuating member 20 to cause rotation of the member 20 in a clockwise direction about the pivot pin 22 when the member 20 is released by the primary bimetal member in a manner hereinafter described.

The thermally responsive device for controlling the actuating member 20 comprises a primary bimetal 36 mounted on a boss 3| of the housing H). The primary bimetal member 36 is carried upon a pin 32 and is thermally connected therewith to receive heat from a heating element 33 having one end thereof connected to the stud 34 and the opposite end to a connector 35. A connector 36 is engaged by the stud 34.

Thus, as can be seen in Fig. 1, electric current may be conducted through the electric motor l4 from the power line Li, through the contacts 12 and I3, thence through the connector 34, heating element 33, connector to the power line L2.

The heating element 33 is thus responsive to current flow through the electric motor l4 and thus responsive to the load carried by the electric motor.

In normal operation, the bimetal member 3|] is thermally sensitive to heat conducted to it through the stud 32 and is thus responsive to the current load through the electric motor 14. The bimetal member 30 will deflect downwardly, as

viewed in Fig. l, to release the actuating device 20 and allow it clockwise rotation to move the operating member E6 in a leftward direction and break circuit through the electric motor by release of the bridging element Hi from the con tacts l2 and [3.

To modify the action of the primary bimetal member 30 there is provided a secondary bimetal member 40 mounted upon the boss 3i and parallel to the primary bimetal member 30. The boss 3| of the housing I!) forms a heat insulating barrier between the bimetal member 30 and the bimetal member 4%. However, the secondary bimetal member 40 is formed to engage primary bimetal member 30 at a point 4| as indicated in Fig. 1. The secondary bimetal member 40 bends in an upwardly direction as viewed in Fig. 1 to modify the action of the primary bimetal member 30.

To limit the modifying movement of the primary bimetal member 38 there is provided a stop member 45a that is carried on an arm 45 extending from the boss 3|. The member 45 limits the upward movement or the primary bimetal member 30, and thus the degree of modification that can be effected for the secondary bimetal member irrespective of the maximum heat transfer to the secondary bimetal member.

In Fig. 2, the thermally responsive device, including the bimetal members 30 and 4D, is illustrated in normal position. In this condition the bimetal member 30 has a slight tendency to move upwardly that is limited by engagement of the member 3&3 with the free end of the bimetal member 48. This position of the free end 46 of the bimetal member 30 relative to the free end 41 of the actuating device 20 is such that a small temperature rise of the bimetal member 30 will cause release of the actuating member 20 from the primary bimetal member 39, as illustrated in Fig. 3.

The aforesaid release of the actuating member 20 is that occasioned by a quick rise in temperature of the bimetal member 30 resulting from a high surge of current through the electric motor I4 representing high overload condition or a walled condition.

At this time of operation of the primary bimetal member 3il on high overload condition of electric motor 14 causing quick release of the actuating device 28, the secondary bimetal member 40 will not be affected as its only thermal connection is through the bimetal member 30 and is insufficient to provide for flexing of the secondary bimetal member in the time of response of the primary member during the quick temperature rise of the primary bimetal member resulting from a high surge current through the heating element 36-33.

However, when the overload condition and the electric motor I4 is such that the current flow is insufiicient to cause the initial temperature rise of the primary bimetal member 39 yet it is sufficient to result in a final temperature rise of the motor to cause such a prolonged overload condition it is essential that the primary bimetal member ultimately provide for release of the actuating device 20 to break circuit through the contacts i2 and [3.

To provide for such delayed action or" the thermal overload and yet a positive action of the primary bimetal member 30, the secondary bimetal member 49 receiving its actuating heat through and from the primary bimetal member 30 will cause a resetting of the free end 46 of the primary bimetal member 30 relative to the free end 41 of the actuating device 20, as illustrated in Fig. 4. This repositioning results from upward deflection of the secondary bimetal member 40 as heated from the primary bimetal member 30. When the overload condition remains on the electric motor a suiiicient period of time, the temperature of the primary bimetal member 30 will ultimately rise to a point at which the deflection of the bimetal member 30 is suiiicient to release the actuating member 20 as illustrated in Fig. 5. The stop member 45 limits the maximum upward deflection of the bimetal member 30 and thus the maximum modification of the member 30 by the secondary bimetal member 40. After the secondary bimetal member 40 has caused modification of the setting of the primary bimetal member 30 by deflection of the bimetal member 40, as illustrated in Fig. 1, further heating of the bimetal member 40 will be ineffective for any further modification of the setting of the bimetal member 30 as limited by the stop member 45.

It will thus be seen that there is provided in one mechanism an arrangement for a quick release of the thermal overload control mechanism or a delayed action release or the control mechanism determined by the type of overload and the volume of the current drawn by the electric motor I 4.

In Fig. 6, there is illustrated a slightly modified arrangement of the structure illustrated in Figs. 1 to 5, inclusive, wherein the primary bimetal member 300 is thermally sensitive to current load through the electric motor l4 resulting from the bimetal member 300 carrying the current. The structure in Fig. 6 is comparable to that heretofore described so that corresponding elements are given the same numbers as heretoiore referred to, but with the sufiix a.

In the modification (Fig. 6) the primary bimetal member 300 is connected directly to the connector 36a at one end thereof and a flexible connection 30! is provided for connecting the opposite end of the bimetal member 300 to the connector 35a, thus being electrically in circuit with the electric motor l4.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form,

it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow:

What is claimed is as follows:

1. In a safety control switch for breaking electric circuit to an electrically operated device in response to electric current now to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active to actuate the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally affected by the electric current flow to the electrically operated device to render said actuating means active to open said contacts, said thermally responsive means com.- prising a primary thermally responsive bimetal element connected with said actuating means; normally detaining the same from actuation and directly releasing the same upon a temperature rise of the said primary element and a secondary thermally responsive bimetal element connected with and responsive to temperature rise of said primary element to modify the action of said primary element to delay release of said actuating means by the said rimary element, said secondary bimetal element being thermally connected with said primary element in a manner to effect slow temperature response of said secondary element from said primary element whereby to eifect modification of said primary element only during a slow temperature rise of said primary element as distinguished from a rapid temperature rise of said primary element resulting from a sudden surge of current to the electrically operated device.

2. In a safety switch for breaking electric circuit to an electrically operated device in response to electric current ilow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active to actuate the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally aifected by the electric current flow to the electrically operated device to render said actuating means active to open said contact means, said thermally responsive means comprising a primary thermally responsive bimetal element connected with said actuating means normall'y detaining the same from actuation and directly releasing the same upon a temperature rise of the said primary element and a secondary thermally responsive bimetal element connected with and responsive to temperature rise of said primary element to modify the action of said primary element to delay release of said actuating means by the said primary element, said secondary bimetal element being thermally connected with said primary element in a manner to eflect slow temperature response of said secondary element from said primary element whereby to effect said modification of said primary element only during a slow temperature rise of said primary element as distinguished from a rapid temperature rise of said primary element resulting from a sudden surge of current to the electrically caperated device and a stop member engageable by said primary element to limit modification movement of said primary element by said secondary element relative to said actuating means.

3. In a safety control switch for breaking electric circuit to an electrically operated device in response to electric current flow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active to actuate the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally in active and thermally responsive to the electric current flow to the electrically operated device to render said actuating means active to open said contact means, means comprising a primary thermally responsive bimetal element connected with said actuating means for normally detaining the same from actuation and thermally deflectable in one direotion to directly releasing the same upon a temperature rise of the primary element and a secondary thermally responsive element connected with said primary bimetal element and thermally defiectable opposite to said primary element to modify the position of said primary element relative to said actuating means to delay release 0i said thermally responsive said actuating meansby the said primary element, said secondary element being thermally connected with said primary element in a manner to eifect slow temperature response of said secondary element from said primary element whereby to effect said position modification of said primary element only during a slow temperature rise of said primary element.

' 4. In a safety control switch for breaking electric circuit to an electrically operated device in response to electriccurrent flow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active, actuating the contact means to open electric circuit therewith, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally affected by the electric current flow to the electrically operated device to render said actuating means active to open said contact means, said thermally responsive means comprising a primary thermally responsive bimetal element temperature sensitive to current flow conducted therethrough to the electrically operated device and connected with said actuating means to normally detain the same from actuation and defiectable in response to the current conducted therethrough to release the said actuating means in response to a temperature rise of the said primary element effected by the current flow to the electrically operated device and a secondary thermally responsive bimetal element indirectly temperature-sensitive to the current flow through thermal connection with said primary element to modify the position of said primary element relative to said actuating means to delay release of said actuating means by the said primary element, said secondary element being thermally connected with said primary element in a manner to effect slow temperature response of said secondary element from said primary element whereby to effect said position modification of said primary element only during a slow temperature rise of said primary element as distinguished from a rapid temperature rise of said primary element resulting from a sudden surge of current to the electrically operated device.

5. In a safety control switch for breaking elecr tric circuit to an electrically operated device in response to electric current flow to the device, the combination of contact means for controlling flow of electric current to an electrically operated device, actuating means said contact means and normally tending to be active actuating the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally aiiected by the electric current flow to the electrically operated device to operably connected with render said actuating means active to open said contact means, said thermally responsive means having a primary thermally responsive element deflectible in one direction upon a rise in temperature thereof and connected with said actuating means for normally detaining the same from actuation and for directly releasing the actuating means upon a temperature rise of said primary element and a secondary thermally responsive element defiectible in a direction opposite to that of said primary element upon a temperature rise in the same and connected with said primary element for temperature response of current to the electrically operated thereto to modify the action of said primary element by deflection of said secondary element in response to temperature rise thereof from said primary element to delay release of said actuating means by the said primary element, said secondary element being thermally connected with said primary element for sponse of said secondary element relative to said primary element whereby to effect said modification of said primary element only during a slow temperature rise of said primary element as distinguished from a rapid temperature rise of said primary element resulting from a sudden surge of current to the electrically operated device.

6. In a safety control switch for breaking electric circuit to an electrically operated device in response to electric current flow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active, actuating the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally affected by the electric current flow to the electrically operated device to render said actuating means active to open said contact means, said thermally responsive means having a primary thermally responsive element defiectible in one direction upon a rise in temperature thereof and connected with said actuating means for normally detaining the same from actuation and for directly releasing the actuating means upon a temperature rise of said primary element anda secondary thermally responsive element defiectible in a direction opposite to that of said primary element upon a temperature rise in the same and connected with said primary element for temperature response thereto to modify the action of said primary element by deflection of said secondary element in response to temperature rise thereof from said primary element to delay release of said actuating means by the said primary element, said secondary element being thermally connected with said primary element for slow temperature response of said secondary element relative to said primary element whereby to effect said modification of said primary element only during a slow temperature rise of said primary element as distinguished from a rapid temperature rise of said primary element resulting from a sudden surge device, and stop means engageable by said primary element to limit the modification movement of the said primary element irrespective of the temperature rise in said secondary element.

7. In a safety control switch for breaking electric circuit to an electrically operated device in response to electric current flow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active to actuate the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally affected by the electric current flow to the electrically operated device to render said actuating means active to open said contact means, said thermally responsive means comprising a primary temperature sensitive bimetal member thermally responsive to ourslow temperature rerent flow to the electrically operated device and engaging said actuating means for normally detaining the same from actuation and for directly releasing the same upon a temperature rise of said primary element, a secondary temperature sensitive bimetal member disposed adjacent said primary member and at least partially heat-insulated from the same but engaging the said primary member for temperature response therefrom said secondary member deflecting in a direction opposite to that of said primary member whereby to effect modification of the point of engagement of said primary member with said actuating means to delay release of said actuating means by said primary member, said secondary member having slow temperature response from said primary member whereby to affect said modification of said primary member only during a slow temperature rise of said primary member as distinguished from a rapid temperature rise of said primary member resulting from a sudden surge of current to the electrically operated device.

8. In a safety control switch for breaking electric circuit to an electrically operated device in response to electric current flow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active to actuate the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally affected by the electric current flow to the electrically operated device to render said actuating means active to open said contact means, said thermally responsive means comprising a primary temperature sensitive bimetal member thermally responsive to current flow to the electrically operated device and engaging said actuating means for normally detaining the same from actuation and for directly releasing the same upon a predetermined temperature rise of said primary element, a secondary temperature sensitive bimetal member disposed adjacent said primary member and temperature sensitive to said primary member for temperature response therefrom, said secondary member deflecting in a direction opposite to that of said primary member whereby to effect modification of the release of said actuating means by said primary member to a second and higher predetermined temperature, said primary member causing release of said actuating means on said first predetermined temperature rise completely independent of said secondary member, said secondary member causing said modification of said primary member only during a slow temperature rise of said primary member as distinguished from a rapid temperature rise of the primary member resulting from a sudden surge of current to the electrically operated device.

9. In a safety control switch for breaking electric circuit to an electrically operated device in response to electric current flow to the device, the combination of, contact means for controlling flow of electric current to an electrically operated device, actuating means operably connected with said contact means and normally tending to be active to actuate the contact means to open electric circuit therethrough, and thermally responsive means operably connected with said actuating means to maintain the same normally inactive and thermally affected by the elec tric current flow to the electrically operated device to render said actuating means active to open said contact means, said thermally responsive means comprising a primary temperature sensitive bimetal member thermally responsive to current flow to the electrically operated device and engaging said actuating means for normally detaining the same from actuation and for directly releasing the same upon a predetermined temperature rise of said primary element, a secondary temperature sensitive bimetal member disposed adjacent said primary member and temperature sensitive to said primary member for temperature response therefrom, said secondary member deflecting in a direction opposite to that of said primary member whereby to effect modification of the release of said actuating means by said primary member to a second and higher predetermined temperature, said primary member causing release of said actuating means on said first predetermined temperature rise completely independent of said secondary member, said secondary member causing said modification of said primary member only during a slow temperature rise of said primary member as distinguished from a rapid temperature rise of the primary member resulting from a sudden surge of current to the electrically operated device, and stop means engageable by said primary member to limit the degree of modification thereof by said secondary member irrespective of the maximum temperature rise of said secondary member.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,496,135 Sedwitz Jan. 31, 1950 2,567,361 Bean Sept. 11, 1951 2,635,156 Welter Apr. 14, 1953 

